The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device.
In a conventional process of manufacturing a semiconductor device, there is adopted a method of forming trenches and via holes in an insulating film by etching, embedding metal layers in the formed the trenches and the via holes and forming interconnect.
Shapes of the trenches and the via holes (hereinafter referred to as “trenches or the like”) are conventionally controlled based on an etching time, but the control based on an etching time involves a problem that it is difficult to accurately grasp the shapes of the trenches or the like. Japanese Patent Laid-Open No. 2006-295171, for example, discloses a method to form interconnect by via-first method.
Japanese Patent Laid-Open No. 2006-073701 discloses a monitoring method of etching rate by optical microscope when a film with mask is etched to expose an underlying another film.
Japanese Patent Laid-Open No. 2003-229414, Japanese Patent Laid-Open No. 2002-93870, National Publication of International Patent Application No. 2006-506812 and National Publication of International Patent Application No. 2006-518942 disclose a method of irradiating light onto trenches or the like and grasping shapes of the trenches or the like from reflected light (e.g., scatterometry method, OCD (Optical Critical Dimension) measurement. Scatterometry method (or OCD measurement) generally includes both single wavelength—multi angle optical scattering method and multi-wavelength—single angle optical scattering method one.
For example, Japanese Patent Laid-Open No. 2003-229414 and Japanese Patent Laid-Open No. 2002-93870 disclose a method of irradiating light onto an insulating film in which a trench or the like is formed and detecting reflected light from the insulating film. The shape of the trench is grasped based on intensity of this reflected light.
According to this method, an interconnect layer is disposed below the trench to be measured. The shape of the trench is measured using light of a wavelength-band in which the utilized wavelength is larger than twice the wiring space of the interconnect layer below the trench to be measured. This inhibits the light from passing through the interconnect layer and prevents the unfavorable reflection from the materials and/or features underlying the interconnect layer.
For example, the interconnect layer is composed of a striped tungsten metal film having a width of 175 nm, thickness of 250 nm and a pitch of 350 nm, and the wiring space is assumed to be 175 nm The wavelength-band of light used for measurement is assumed to be 900 nm to 1600 nm.
However, the present inventor found out that the measuring methods disclosed in the related arts have the following problems.
When forming an interconnect layer, a trench is formed in an insulating film, this trench is filled with a metal film, the metal film is then polished and removed by CMP (Chemical Mechanical polishing). In this case, erosion occurs as shown in FIG. 6.
In FIG. 6, reference numeral 901 denotes an insulating film, 902 denotes a metal film, 903 denotes an etching stopper film, 904 denotes an interlayer insulating film and 905 denotes a cap film.
As shown in FIG. 6, steps are produced on the surface of the cap film 905 at the top of the interconnect layer and the surface undulates due to the influence of erosion.
When a trench is formed in such a condition, as shown in FIGS. 7A and 7B, the shape of the trench 906 varies a great deal due to a difference in positions at which the opening of a mask is formed. Therefore, it is difficult to fix the measuring condition of the trench 906 to a certain condition, which affects productivity.
Furthermore, since the steps are produced on the surface of the cap film 905 due to the influence of erosion, the steps remain on the surface of the cap film 905 even after the trench 906 is formed. In this case, the measuring light is reflected by the steps and erroneous information is likely to occur when the trench 906 is measured.